Targeted transport of cellular constituents to specific locations is an essential function for normal activity and growth in every eukaryotic cell type. The three motor families, myosins, dyneins and kinesins, cooperate in directing cargoes along microtubules and the actin cytoskeleton. Although multiple motors are required to confer bidirectional motion and to switch between these cytoskeletal tracks, the coordination and competition between them is not understood. Many of the molecular motors are regulated by Ca 2+, phosphorylation, or recruitment to their sites of action by protein scaffolds. The domains that target the motor proteins, the scaffolds that assemble the specific linkages between motors and cargoes, and the chemistry of association between macromolecular motors and lipids are major open questions. Novel biophysical, molecular, and cell biological techniques developed for earlier studies open exciting opportunities for understanding targeted intracellular transport. In this program project, the actin-based motors, myosin I, myosin V and myosin VI, and the microtubule-based motor, cytoplasmic dynein, and its accessory protein complex, dynactin, will be studied intensively by a battery of state-of-the-art approaches. Single-molecule fluorescence polarization, nanometer-resolved fluorophore localization, infrared optical traps, rapid biochemical reaction kinetics, nanosecond time-resolved fluorescence anisotropy, dynamic light scattering, genetic manipulations, and detailed electron and atomic force microscopy will be applied in collaborative studies to understand the individual mechanisms of molecular motors and their mutual interactions. An understanding of the assembly process of every cell, including the muscle sarcomere and cytoskeleton, will require an in-depth study of the function of a number of different motor proteins. As cell proliferation, assembly, protein expression, motility, energy metabolism, defense, nourishment, and secretion all involve such localized motor-driven complexes, the impact of understanding the mechanisms and control of targeted intracellular transport spreads across all of cell biology. Cancer invasion and metastasis, neuronal and muscle development, pathogen attack by host defenses and many other systems make extensive use of the same molecular motors. Thus, detailed understanding of the function and interaction of these proteins have specific and broad-reaching implications in human disease and treatment. We will discover how motor proteins, dynein and unconventional myosins work individually and in brother/sisterhood.